A disk drive is disclosed comprising a head actuated over a disk, a spindle motor operable to rotate the disk, and control circuitry comprising a speed control loop operable to control a rotation speed of the disk. A rotation speed of the disk is measured, and a speed error is generated in response to the measured rotation speed. The speed error is processed with a compensator to generate a control signal, a disturbance is injected into the control signal to generate a modified control signal, and the modified control signal is applied to the spindle motor. An amplitude of the disturbance is ramped, and after ramping the amplitude of the disturbance, an open-loop gain of the speed control loop is estimated at a frequency of the disturbance, and at least one parameter of the compensator is adjusted in response to the estimated open-loop gain.
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1. A disk drive comprising:
a disk;
a head actuated over the disk;
a spindle motor operable to rotate the disk; and
control circuitry comprising a speed control loop operable to:
measure a rotation speed of the disk;
generate a speed error in response to the measured rotation speed;
process the speed error with a compensator to generate a control signal;
inject a disturbance into the control signal to generate a modified control signal; and
apply the modified control signal to the spindle motor;
wherein the control circuitry is operable to:
ramp an amplitude of the disturbance while injecting the disturbance into the control signal; and
after ramping the amplitude of the disturbance, estimate an open-loop gain of the speed control loop at a frequency of the disturbance and adjust at least one parameter of the compensator in response to the estimated open-loop gain.
10. A method of operating a disk drive, the disk drive comprising a head actuated over a disk, a spindle motor operable to rotate the disk, and control circuitry comprising a speed control loop operable to control a rotation speed of the disk, the method comprising:
measuring a rotation speed of the disk;
generating a speed error in response to the measured rotation speed;
processing the speed error with a compensator to generate a control signal;
injecting a disturbance into the control signal to generate a modified control signal; and
applying the modified control signal to the spindle motor;
ramping an amplitude of the disturbance while injecting the disturbance into the control signal; and
after ramping the amplitude of the disturbance, estimating an open-loop gain of the speed control loop at a frequency of the disturbance and adjusting at least one parameter of the compensator in response to the estimated open-loop gain.
2. The disk drive as recited in
3. The disk drive as recited in
4. The disk drive as recited in
where:
Kp represents the gain of the compensator; and
OLGi represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to Kp[i].
5. The disk drive as recited in
where:
Kp represents the gain of the compensator;
OLGi represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to Kp[i]; and
α is a positive scalar less than one.
6. The disk drive as recited in
where:
Kp represents the gain of the compensator;
ωolbw is a desired bandwidth frequency of the speed control loop;
Kd is a gain of a spindle motor driver operable to drive the spindle motor;
Kt represents a motor torque constant of the spindle motor;
Ke represents a back electromotive force constant of the spindle motor;
Jspindle represents a total rotational inertia of the spindle motor;
Rw represents a winding resistance of the spindle motor; and
Ki represents a ratio of an integral gain to a proportional gain of the compensator.
7. The disk drive as recited in
8. The disk drive as recited in
where:
Kp represents the gain of the compensator;
ωolbw is a desired bandwidth frequency of the speed control loop;
Kd is a gain of a spindle motor driver operable to drive the spindle motor;
Kt represents a motor torque constant of the spindle motor;
Ke represents a back electromotive force constant of the spindle motor;
Jspindle represents a total rotational inertia of the spindle motor;
Rw represents a winding resistance of the spindle motor; and
Ki represents a ratio of an integral gain to a proportional gain of the compensator.
11. The method as recited in
12. The method as recited in
13. The method as recited in
where:
Kp represents the gain of the compensator; and
OLGi represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to Kp[i].
14. The method as recited in
where:
Kp represents the gain of the compensator;
OLGi represents the estimated open-loop gain of the speed control loop at the frequency of the disturbance corresponding to Kp[i]; and
α is a positive scalar less than one.
15. The method as recited in
where:
Kp represents the gain of the compensator;
ωolbw is a desired bandwidth frequency of the speed control loop;
Kd is a gain of a spindle motor driver operable to drive the spindle motor;
Kt represents a motor torque constant of the spindle motor;
Ke represents a back electromotive force constant of the spindle motor;
Jspindle represents a total rotational inertia of the spindle motor;
Rw represents a winding resistance of the spindle motor; and
Ki represents a ratio of an integral gain to a proportional gain of the compensator.
16. The method as recited in
17. The method as recited in
18. The method as recited in
where:
Kp represents the gain of the compensator;
ωolbw is a desired bandwidth frequency of the speed control loop;
Kd is a gain of a spindle motor driver operable to drive the spindle motor;
Kt represents a motor torque constant of the spindle motor;
Ke represents a back electromotive force constant of the spindle motor;
Jspindle represents a total rotational inertia of the spindle motor;
Rw represents a winding resistance of the spindle motor; and
Ki represents a ratio of an integral gain to a proportional gain of the compensator.
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Disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and embedded servo sectors. The embedded servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a VCM servo controller to control the velocity of the actuator arm as it seeks from track to track.
A spindle motor typically in the form of a brushless DC motor spins the disk during normal access operations. The speed of the spindle motor is maintained using a speed control loop which measures a speed error, and then filters the speed error with a suitable compensator (e.g., a proportional-integral (PI) compensator). The ability of the speed control loop to maintain the disk at the target speed typically depends on the performance characteristics of the spindle motor, as well as the parameter settings of the compensator (e.g., the gain setting which affects the bandwidth of the speed control loop).
In the embodiment of
Adjusting at least one parameter of the spindle motor compensator 42 in response to the estimated open-loop gain helps optimize performance of the speed control loop and thereby help maintain the target rotational speed of the disk during normal operation. Injecting a disturbance 46 into the control signal 44 of the speed control loop enables the control circuitry 22 to estimate the open-loop gain at the frequency of the disturbance 46. In an embodiment of the present invention, the control circuitry 22 first optimizes the amplitude of the disturbance 46 prior to injecting the disturbance 46 into the speed control loop. This is illustrated in the flow diagram of
Any suitable parameter of the compensator 42 may be adjusted at block 36 of
where:
After initializing the gain of the compensator 42 (block 62), the disk 18 is spun-up to a target speed (block 64), and the amplitude of the disturbance 46 is ramped until an optimal amplitude is determined (block 66). The disturbance 46 is injected into the control signal 44 of the speed control loop (block 68), and the open-loop gain of the speed control loop is estimated at a frequency of the disturbance 46 (block 70). If the estimated open-loop gain of the speed control loop does not substantially match a target (block 72), and a maximum number of retries has not been reached (block 74), then the gain of the compensator 42 is adjusted (block 76) and the flow diagram is repeated from block 68. When the open-loop gain of the speed control loop substantially matches the target (block 72), then the compensator 42 is configured with the adjusted gain (block 78). If the maximum number of retries is reached (block 74), then the compensator 42 is configured with a default gain (block 80). In one embodiment, the default gain used to configure the compensator 42 at block 80 is the nominal gain configured at block 62 described above.
The open-loop gain of the speed control loop may be estimated at the frequency of the disturbance 46 using any suitable technique. In one embodiment, the open-loop gain may be estimated according to:
where CTL_SIG is the control signal 44, DISTURBANCE is the disturbance 46 injected into the control signal 44, and DFT is a Discrete Fourier Transform.
The gain of the compensator 42 may be adjusted at block 76 of
where:
where:
Any suitable control circuitry may be employed to implement the flow diagrams in the embodiments of the present invention, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into an SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
Yang, Wenli, Smith, Brandon P.
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